Abrasive article and method of manufacturing the same



Patented July 12, 1927.

UNITED STATES PATENT OFFICE.

LOWELL HAINES MILLIGAN AND CHARLES HERBERT QUICK, OE WORCESTER, MASSA- CHUSETTS, ASSIGNORS T NORTON COMPANY, OF WORCESTER, MASSACHUSETTS, A i

CORPORATION OI MASSACHUSETTS.

ABRASIVE ARTICLE AND METHOD OI MANUFACTURING THE SAME.

No Drawing.

This invention relates to the manufacture of a new and improved ceramic bonded abrasive-article containing crystalline alumina, and more particularly to a grinding Wheel containing crystalline alumina united by a vitrified bond.

In the manufacture of abrasive articles made of granular refractory and abrasive materials bonded by ceramic materials, such 1 grinding wheels, it is customary to shape the green articles of granular abrasive grains mixed with a plastic clay bond and then fire this relatively fragile and soft mass in a kiln at a temperature approximately 1300" C. to vitrify thebond.

Grinding wheels containing alumina granules united by a vitrified bond often have a brown color throughout. At times, however, the color of the wheels, which normally would be brown. as they come from the ceramic kilns in which they are fired is bluish or blue-mottled, and such wheels are said to be blue-stoned. A blue-stoned wheel is considered harder by many users of grinding wheels and more satisfactory for certain purposes than a wheel havin a brown color. This has created a deman for bluestoned wheels for certain grinding operations.

The-manufacturers have had considerable difliculty in supplying this demand inasmuch as the blue-stoned wheel has been produced incidentallyor accidentally under unknown conditions during the manufacture of the brown wheels. The blue-stoned wheels could not be produced on a large scale, nor could their characteristics be controlled and duplicated at will. Furthermore, many of the blue-stoned wheels actually produced heretofore have been unmarketable because of their tendency to be defective, or to'have a faulty structure containing blisters.

' One of the objects of our invention -is to provide an abrasive article of aluminous ma terial bonded by a vitrified ceramic material having certain characteristics and particularly an abrasive article which is in what is known as the blue-stoned condition.

A further object is to provide a method of manufacturing an aluminous abrasive article of uniform and desired properties which insures the reproduction of such an article at will and in commercial quantities.

Application filed September 4, 1825. Serial No. 54,582.

As a result of extended investigations, we have discovered that some changes may take place in the character of certain bond constituents during firing of ceramic .articles, suchas grinding wheels, to soften and mature the bond, which materially affeet the properties and character of the tinished article. In particular, it has been no ticed that in the preliminary stages of the tiring operation, if the bond constituents are subjected to oxidizing influences, carbonaceous material present is oxidized and driven off in the form of carbon monoxide and carbon dioxide gas. Also, any iron present in the bond mixture is oxidized to ferric oxide, if not already present in that form, during the preliminary stages of the iiring operation. This ferric oxide may be dissociated during a later stage of the firing operation While the bond is being softened. Thus, ferric oxide may dissociate. to form ferroso-ferric oxide and oxygen. -After the bond has softened, crystallization of one or more of its constituents may take place during coolin As a result of these discoveries, we Iiave found that a blue-stoned wheel may be pm duced instead of a brown wheel by firing the article in any appropriate manner, but preferably by. subjecting the article to oxidizing influences during the early part of the firing, and thereafter cooling the article in a nonoxidizing environment or while protected from the action of the furnace gases. This may be accomplished in various ways.

For example, the article may be packed in a material such as granular hematite or hematite mixtures which will not interfere with oxidization during the early part of the burn, but at higher temperatures will dissociate to magnetite and absorb oxygen from the air during cooling, thereby preventing oxidation of the article or its bond constituents. If desired, the article may be fired under oxidizing conditions during the heat ing-up period and the kiln atmosphere as a whole may be then made non-oxidizing by displacing the air with nitrogen, or by other suitable means.

In accordance with the preferred practice of the invention, however, the article is coated with a material which does not in terfere with the oxidation of the oxidizable constituents of'the bond, yet is adapted to fuse as the bond constituents are softened, or during the soaking period in the kiln, to form a coating which is substantially impervious to gases and thereby protect the bond constituents during cooling to solidification.

It will be apparent to those skilled in the stoned grinding wheels having uniformly similar properties may be-produced with regularity by mixing crystalline alumina granules with an appropriate bond mixture consisting of fusible clays, feldspar-s and so forth, and containing, say roughly, four per cent of ferric-oxide. This mixture is then shaped as desired in accordance with any wel known method. The thus shaped article 131211811 coated with a suitable coating mixture capable of fusing at the temperature of firing the abrasive article.

An example of. such a coating is one con sisting largely of feldspar, which may be combined with other ingredients, such as ball clay and lime. A suitable mixture is one containing about 82% of ground feldspar, about'15% of plastic ball clay, and about 3% of lime.

- The thus coated article is then dried and fired to vitrify the bond mixture. It will be apparent, therefore, that the oxygen of the furnace gases is permitted to penetrate the pervious to the kiln gases.

coating while it is still porous during the heating-up in the kiln, and subject the bond mixture to oxidizing influences for a sufii cient length of time for the purposes of the invention. The coating composition fuses in the neighborhood of the dissociation temperatures of ferric-oxide and forms a glaze or glassy covering which is substantially im- The article is then permitted to cool slowly and is protected during this cooling by the fused coating composition which keeps the furnace gases out of contact with the bond constituents. By conducting the firing operation in this manner ferroso-ferric oxide or magnetite is formed or maintained in the bond and may partially crystallize within it. The

ferroso-ferric oxide crystals have a blue or bluish-black color which is imparted to the grinding wheel. The color of the finished article may-be affected to some extent by the fact that a portion of the iron may be resent in forms more reduced than ferrosoerric oxide.

In accordance with the provisions of the invention, auniformly blue-stoned abrasive abrasive article canbe produced upon a commercial. scale in such quantities as are desired and having characteristics sought by the trade.

tity desired, articles having uniformly similar characteristics and properties, and 1111b form throughout in appearance and composition.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent is:

1. The improvement in the manufacture of abrasive articles containing alumina and a vitrifiable bond mixture which comprises firing the article to soften the bond mixture, and thereafter cooling the bond constituents to solidification undernouoxidizing conditions.

2. The improvement in the manufacture of articles containing crystalline alumina and a vitrifiable bond mixture which comprises firing the article in an oxidizin environment to soften the bond mixture, an thereafter cooling the bond constituents to solidification under non-oxidizing conditions.

3. The improvement in the manufacture of an abrasive article containing crystalline alumina and a vitrifiable bond mlxture which comprises firing the article invan oxidizing environment to mature the bond mixture, and thereafter cooling the article while preventing contact thereof with the oxidizing gases.

4. The

alumina bonded-b a vitrifiable mixture containing'iron whic comprises firin the article to soften'the bond, and therea ter cooling the bond mixture to solidification, said firing and cooling operations being so conducted that the iron present in the bond is disassociated and thereafter maintained in a non-oxidizing atmosphere.

5. The improvement in the manufacture of an abrasive article of crystalline alumina bonded by a vitrifiable mixture containing iron which comprises appropriately firin the article to soften the bond mixture, and cooling the bond constituents to solidification in a substantially non-oxidizing atmosphere, said firing and cooling operations being conducted under conditions favorable to the formation of'crystals of ferroso-ferric oxide.

6. The improvement in the manufacture of an abrasive article containing crystalline alumina and a vitrifiable bond mixture which comprises applying a suitable porous coating of fusible ceramic material on the article, firing the article to mature the bond and fuse the coating so as to render the coating substantially impervious to the furcrystalline improvement in the manufacture of an abraslve article containing crystalline i in an oxidizing environment, firing the article to mature the bond and fuse the coating so as to render the coating substantially impervious to the furnace gases, and cooling the article to solidification while thus protected.

8. The improvement in the manufacture I of an abrasive 'articlecontainin crystalline alumina and a vitrifiable bond mixture which comprises applying on the article a! porous coating composed in large part of ground felds ar, firing the article to soften the bond and use the coating 'to render the same substantially im ervious to the furnace gases, and cooling t e bond constituents to solidifica'tion while thus protected.

9. An article of manufacture containing crystalline alumina granules united by a ceramic bond which has been vitrified by fir-- ing the article under oxidizing conditions -to soften the bond and then cooled to solidify the bond under non-oxidizing conditions.

10. An abrasive article containing crystalline alumina granules united by a vitrified ceramic bond containing iron principally in the form of magnetite, the ingredients being of a composition such that a brown color may be imparted to the article byfiring in an oxidizing environment. I

Signed at Worcester, Massachusetts, this 3rd day of Sept. 1925.

LOWELL HAIN-ES .MILLIGANQ CHARLES HERBERT QUICK. 

